Estimating the natural rechargeis essential to the study of the ground water resources, as well as to any effective resource management. In order to establish the ground water natural recharge rate at Santa Maria, the easternmost island of the Azores archipelago, a daily water balance model was developed. The amount of recharge in the studied period range from 2429814 m3 to 4603418 m3, and the recharge rate varies from approximately 14% to 15%. The comparison with the natural recharge rate estimation made by the chloride balance method shows a good agreement between both techniques, and therefore suggests the coupled application as a tool for results validation.